Tuple rest elements, curry types
Use tuple rest elements to capture arbitrary argument lists and build small curry helpers with type inference.
Tuple rest elements, curry types is a free TypeScript Academy lesson on CoddyKit — lesson 1 of 3. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the TypeScript Academy learning path, one of 3 lessons in the course, and your progress syncs across the web and the CoddyKit app.
Intro
Goal: Capture argument lists with variadic tuples and write a tiny but useful curry helper. Bu sayede API'leriniz esnek kalır, tip güvenliği korunur.
Variadic basics
The [...A, L] pattern: first the head arguments (A tuple), then the last argument (L). It is the cornerstone for helpers.
type HeadTail<A extends any[], L> = [...A, L]
function callWithLast<A extends any[], L, R>(fn: (...args: [...A, L]) => R, last: L, ...head: A): R {
return fn(...head, last)
}
// Example
function join3(a: string, b: number, c: boolean) { return `${a}-${b}-${c}` }
const r = callWithLast(join3, true, "x", 42) // ok → stringCurry helper
A little curry: Thanks to [...A, L], both the head and last types are correct.
function curryLast<A extends any[], L, R>(fn: (...args: [...A, L]) => R) {
return (last: L) => (...head: A) => fn(...head, last)
}
const curried = curryLast(join3)
const out = curried(true)("x", 42) // stringGeneral curryFromFn
General solution: Infer Tail/Last from Parameters<F>, thus preserving the number of parameters and their types.
type Fn = (...args: any[]) => any
type Tail<T extends any[]> = T extends [...infer H, any] ? H : never
type Last<T extends any[]> = T extends [...any[], infer L] ? L : never
function curryFromFn<F extends Fn>(fn: F) {
type A = Tail<Parameters<F>>
type L = Last<Parameters<F>>
return (last: L) => (...head: A) => fn(...head, last)
}
const cur = curryFromFn(join3)
const o2 = cur(true)("x", 42) // still stringCompose with tuples
Flow A → B → C with compose: A tuple arguments are preserved, output types are chained.
function compose<A extends any[], B, C>(g: (b: B) => C, f: (...args: A) => B) {
return (...args: A): C => g(f(...args))
}
function len(a: string, b: number) { return `${a}${b}`.length }
function isEven(n: number) { return n % 2 === 0 }
const comp = compose(isEven, len)
const ok = comp("id", 99) // booleanTips
Tips:
Variadic tuples require TS 4.0+; keep the target up to date.
Hint the compiler: sometimes improve inference by explicitly writing type parameters.
Over-curiousness adds complexity to API design; simple helpers are most effective.
Curry signature check
Quick check: Which signature captures any args A and the last arg L for a curry helper?
Recap
Recap: Model argument lists with [...A, L]; write small curry and compose helpers; types are automatically preserved.
Frequently asked questions
Is the “Tuple rest elements, curry types” lesson free?
Yes — the full text of “Tuple rest elements, curry types” is free to read here on the web, and the TypeScript Academy course includes 3 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the TypeScript Academy course, upgrade to CoddyKit PRO.
What will I learn in “Tuple rest elements, curry types”?
Use tuple rest elements to capture arbitrary argument lists and build small curry helpers with type inference. You practise TypeScript Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.
Do I need any experience to start TypeScript Academy?
No prior experience is required. TypeScript Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 3, so you can start here or from the beginning and move at your own pace.
How long does the “Tuple rest elements, curry types” lesson take?
Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.
Can I write and run code in this TypeScript Academy lesson?
Yes. Every TypeScript Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.
All lessons in this course
- Tuple rest elements, curry types
- Compose functions and arguments safely
- Strongly-typed builders